There isn't a lot of stress on .45 ACP brass anywhere except back near the head. So if you're just talking about case mouth dings (the most common ones) don't worry about them until you see an actual crack or split. At that point you toss them, of course. If the head is bent, then it goes in the scrap brass bucket.

For general practice I've picked up and used .45 brass that had been stepped on and left to turn deep brown for a season or two in the mud. Just stick a Philips head screwdriver in and roll the inside open to approximate shape. Gouge out all the dirt and mud and insect nests. Flush and dry if needed. The mouth might come out a little uneven, but hey, this isn't for my match loads. Load and shoot.